A liquid crystal display device (a display device) equipped with a non-light-emitting display panel (a member to be illuminated) typically has a backlight device (an illumination device) that irradiates the display panel with light. A backlight device provided with a plurality of LEDs (Light Emitting Diodes) (light sources) and a light guide plate that guides light from these LEDs is known as such a backlight device.
FIG. 10 is a cross-sectional view showing the structure of one example of a conventional backlight device provided with an LED and a light guide plate. As shown in FIG. 10, one example of a conventional backlight device 1001 is provided with an LED (light source) 1002, a mounting substrate 1003 whereon the LED 1002 is mounted, a light guide plate 1004 that guides light from the LED 1002, a reflective sheet 1005 placed on the back side of the light guide plate 1004, and a plurality of optical sheets 1006 placed on the front side (a light exiting surface 1004b) of the light guide plate 1004. In this backlight device 1001, the light emitted by the LED 1002 is incident on a light incident surface 1004a of the light guide plate 1004, and is emitted towards a not-shown display panel (the member to be illuminated) from the light exiting surface 1004b of the light guide plate 1004.
However, in the backlight device 1001, a portion of the light that is incident on the light guide plate 1004 reaches an opposing surface 1004c that is opposite to the light incident surface 1004a of the light guide plate 1004. If the light that reaches the opposing surface 1004c leaks to outside of the light guide plate 1004, then light is not able to be sufficiently utilized. Therefore, a method is widely used in which a reflective tape (not shown) or the like is provided on the opposing surface 1004c to return the light being emitted to outside from the opposing surface 1004c back to inside the light guide plate 1004 by using the reflective tape or the like.
A portion of the light reflected by the opposing surface 1004c will also be emitted to the LED 1002 side from the light incident surface 1004a of the light guide plate 1004. Light being reflected by the opposing surface 1004c leaking to outside the light guide plate 1004 from the light incident surface 1004a also means that light is not able to be sufficiently utilized. Thus, as shown in FIG. 11, a method was used in which a white layer (white resist or white tape) 1007 is provided on the surface of the mounting substrate 1003 to return the light emitted from the light incident surface 1004a back to inside the light guide plate 1004.
Conventionally, an illumination device that can improve the utilization efficiency of light emitted from the LEDs to some degree has been proposed (see Patent Document 1, for example). A light-emitting device (an illumination device) is disclosed in Patent Document 1 provided with a light-emitting diode (a light source) that emits near-ultraviolet light, a flat plate-like light guide body (a light guide plate) that guides light from the light-emitting diode, an optical filter placed on a light exiting surface of the light guide body, and phosphors (fluorescent members) placed on the light exiting side of the optical filter.
The phosphors in this light-emitting device function to convert near-ultraviolet light into visible light. The optical filter also functions to allow near-ultraviolet light to pass through and reflects visible light. This enables suppression of visible light returning back to the light guide body because the visible light emitted from the phosphors to the light guide body is reflected by the optical filter.